The kinetics of the activity of total creatine kinase (CK) and creatine phosphokinase isoenzyme muscle-brain were investigated in 48 patients with acute myocardial infarction after successful intracoronary thrombolysis, and compared to the enzyme activities in 17 patients in whom thrombolysis failed. CK activity peaked significantly earlier after a successful thrombolysis than after an unsuccessful attempt: in patients with successful thrombolysis, CKmax = 10.5 +/- 3.7 h and in patients with an unsuccessful attempt, CKmax = 19.3 +/- 5.9 h; p less than or equal to 0.05. The area under the activity time curve after successful thrombolysis was significantly smaller than after unsuccessful thrombolysis: in patients with successful thrombolysis, CK area = 25,255 U/l per day and in patients with an unsuccessful attempt, CK area = 32,602 U/l per day; p = 0.015. There was a negative correlation between the area under the CK serum curve after successful thrombolysis, and the change of regional wall motion at the site of the acute infarct (p less than or equal to 0.05). From the smaller area under the CK curve in patients after successful thrombolysis, and the significant negative correlation of this measurement with regional left ventricular wall motion, we conclude that myocardial salvage after intracoronary thrombolysis can be assessed by serial CK measurements.